The northern spotted owl (Strix occidentalis caurina) is one of three spotted owl subspecies. A western North American bird in the family Strigidae, genus Strix, it is a medium-sized dark brown owl native to the Pacific Northwest. An important indicator species, the northern spotted owl remains threatened due to continued population decline from human-caused habitat destruction and competition with invasive species, its main competitor being the barred owl.
Description
Northern spotted owls have dark brown plumage with white spots and no ear tufts. They are typically around sixteen to nineteen inches in length and one to one and one sixth pounds. Females are about 10-20% larger than males. Their wingspan is approximately 42 inches. They are a mainly nocturnal species, and form long-term pair bonds. While most owls have yellow to red-orange colored eyes, northern spotted owls are one of the few owls with darkish to black-colored eyes.
Vocalizations
Thirteen different sounds of hoots, whistles, and barks have been identified to be sounds of the northern spotted owl, with females having higher pitched calls than males. Of the three different styles of calls, hoots appear to be most commonly used to announce things, such as territory and prey. The whistles are often used by the females to present themselves to the males, and the barks during territorial issues between owls.
Distribution and habitat
The northern spotted owl primarily inhabits old growth forests in the northern part of its range (extreme southwestern Canada to southern Oregon) and landscapes with a mix of old and younger forest types in the southern part of its range (Klamath region and California). The subspecies' range is the Pacific coast from extreme southern British Columbia to Marin County in northern California.
Most spotted owls inhabit federal lands (Forest Service, Bureau of Land Management, and National Park Service lands), although significant numbers occur on state lands in Washington, Oregon, and California, as well as tribal and private properties.
Northern spotted owls range on 500,000 acres of the 7.6 percent of private forestlands managed by Native American tribes in the state of Washington. Federally recognized tribes are treated as sovereign governments, and each recognized tribe is responsible for their own management plans for the northern spotted owls in their area. Regardless of tribal or private ownership, however, the United States federal government requires all land owners and inhabitants to comply with the Endangered Species Act.
The northern spotted owl nests in cavities or on platforms in large trees. It will also use abandoned nests of other species. Northern spotted owls remain in the same geographical areas unless forced out from harsh conditions or lack of food.
Diet
The northern spotted owl diet consists of small mammals (91.5%), birds (4.3%), insects (4.1%), and other prey (0.1%). These prey are most nocturnal (91.9%) or active during the day and night (4.8%), which corresponds to the primarily nocturnal nature of the northern spotted owl. The main species consumed by the northern spotted owl are northern flying squirrels (Glaucomys sabrinus), woodrats (Neotoma fuscipes and N. cinerea), red tree voles (Arborimus longicaudus), western red-backed voles (Clethnonomys californicus), deer mice (Peromyscus maniculatus), and gophers (Thomomys spp.). Consumption of these small mammals varies by habitat region and proliferation of small nocturnal mammals. Recent invasion of barred owls (Strix varia) into the northern spotted owl range has resulted in decreased food availability due to overlap in dietary preferences.
Behavior
The northern spotted owl is intolerant of habitat disturbance. Each nesting pair needs a large amount of land for hunting and nesting, and will not migrate unless they experience drastic seasonal changes, such as heavy snows, which make hunting difficult. Their flight pattern is distinct, involving a series of rapid wingbeats interspersed with gliding flight. This technique allows them to glide silently down upon their prey.